Abstract: A reactor fluid supply system, a reactor system comprising such a fluid supply system, a method of supplying fluid into a reactor, and a method of operating a reactor system are provided. Preferably, the reactor system comprises a fluidised bed pyrolysis or combustion reactor and a fluid injector. The injector may comprise an internal flow passage extending from an inlet to an outlet, and have a first section including the inlet and a first portion of the passage and a second section including the outlet and a second portion of the passage. There may be a temperature regulator for controlling fluid temperature in the second section of the injector, the regulator comprising a cooling fluid jacket surrounding the second portion of the internal flow passage. The second section of the injector may be located inside the reactor so that the outlet of the injector is positioned in the fluidised bed of the reactor.